Sorry, been a bit out of touch for a long while, and had a few server changes over time, so just to clear some things up:
I've uploaded version 1.1 to the following location:
http://mariusth.channelwood.org/Files/MacOSigX.sitIt ISN'T a Disk Image but a .sit image that is to be opened with StuffIt Expander, i choose this format so it could be opened on both Classic and OS X, seeing that (Until Tiger) every Mac came shipped with it, and is still freely downloadable on StuffIt's Site: http://www.Stuffit.com

Oh, thank you, thank you, THANK YOU! I'd given up using any SigX on my Mac at all, but if this works, I'll be thrilled to.

That would certainly explain why I couldn't mount the disk image, but it was a .dmg file that I downloaded, with no mention of extraction required, and I've got StuffIt installed on my Mac. Ah well, good to have an explanation, and that may help me out if I run into a similar problem in future.

And welcome back from the world of the disappeared internet user ~ it seemed that you'd fallen off the face of the planet!